UHF.html



Ultra high frequency (UHF) designates a range (band) of electromagnetic waves with frequencies between 300 MHz and 3 GHz (3,000 MHz). Also known as the decimetre band or decimetre wave as the wavelengths range from ten to one decimetres. Radio waves with frequencies above the UHF band fall into the SHF (Super high frequency) and EHF (Extremely high frequency) bands, all of which fall into the Microwave frequency range. Lower frequency signals fall into the VHF (Very high frequency) or lower bands. See electromagnetic spectrum for a full listing of frequency bands.

Uses

UHF and VHF are the most commonly used frequency bands for transmission of television signals. Modern mobile phones also transmit and receive within the UHF spectrum. UHF is widely used by public service agencies for two-way radio communication, usually using narrowband frequency modulation, but digital services are on the rise. There has traditionally been very little radio broadcasting in this band until recently; see digital audio broadcasting for details. The Global Positioning System also uses UHF.

One uncommon use of UHF waves is for the detection of partial discharges. Partial discharges occur because of the sharp geometries created in high voltage insulated equipment. The advantage of UHF detection is that this method can be used to localize the source of the discharge. A drawback to UHF detection is the extreme sensitivity to external noise. UHF detection methods are used in the field, especially for large distribution transformers.

2.45 GHz, now mainly used for WiFi, Bluetooth and US cordless phones has been proposed for Wireless energy transfer. Some pilot experiments have been performed, but it is not used on a large scale.

Amateur radio operators also operate in several UHF bands.

Some radio frequency identification (RFID) tags utilize UHF. These tags are commonly known as UHFID's or Ultra-HighFID's (Ultra-High Frequency Identification) and often are small battery-powered devices such as those used to remotely open doors of motorcars.

Characteristics and advantages

Main article: radio propagation

The point to point transmission of radio waves is affected by many variables. Atmospheric moisture, the stream of particles from the sun called solar wind, and time of day will all have an effect on the signal transmission. All radio waves are partially absorbed by atmospheric moisture. Atmospheric absorption reduces, or attenuates, the strength of radio signals over long distances. The effects of attenuation increases according to the frequency. UHF signals are generally more degraded by moisture than lower bands such as VHF. The layer of the Earth's atmosphere called the ionosphere is filled with charged particles that can reflect radio waves. The reflection of radio waves can be helpful in transmitting a radio signal over long distances as the wave repeatedly bounces from the sky to the ground. UHF benefits less from the effects of reflection than lower (VHF, etc.) frequencies. UHF transmissions may be enhanced by tropospheric ducting as the atmosphere warms and cools throughout the day.

The main advantage of UHF transmission is the physically short wave that is produced by the high frequency. The size of transmission and reception equipment, (particularly antennas), is related to the size of the radio wave. Smaller and less conspicuous antennas can be used with higher frequency bands.

UHF is widely used in two-way radio systems and cordless telephones. UHF signals travel over line-of-sight distances. Transmissions generated by two-way radios and cordless telephones do not travel far enough to interfere with local transmissions. A number of public safety and business communications are handled on UHF. Civilian applications such as GMRS, PMR446, UHF CB, and 802.11b ("WiFi") are popular uses of UHF frequencies. A repeater is used to propagate UHF signals when a distance that is greater than the line-of-sight is required.

• See: Radio horizon

History

Australia

In Australia, UHF was first anticipated in the mid 1970s with TV channels 27 - 69. The first UHF TV broadcasts in Australia were operated by Special Broadcasting Service (SBS) on channel 28 in Sydney and Melbourne starting in 1980, and translator stations for the Australian Broadcasting Corporation (ABC). The UHF band is now used extensively as ABC, SBS, commercial and community (public access) television services have expanded particularly through regional areas.

Australia also provides the UHF CB service for general-purpose two-way communications.

Canada

In Canada and México, channel assignments for VHF and UHF terrestrial television are similar to those of the United States, however most legal requirements that manufacturers include UHF TV or digital television tuners (as applied to the US in the All-Channel Receiver Act of 1961) did not have direct counterparts in Canada or México.

The first Canadian television network was publicly-owned Radio-Canada, the Canadian Broadcasting Corporation. Its stations, as well as that of the first private networks (CTV and TVA, created in 1961), are primarily VHF. More recent third-network operators initially signing-on in the 1970s or 1980s were often relegated to UHF, or (if they were to attempt to deploy on VHF) to reduced power or stations in outlying areas. Canada's VHF spectrum was already crowded with both domestic broadcasts and numerous foreign border stations.

The use of UHF to provide programming which otherwise would not be available, such as province-wide educational services (Knowledge Channel, TV Ontario, Télé-Québec), French language programming (outside Québec) and ethnic/multilingual television, has therefore become common. Third networks such as Quatre-Saisons or Global often will rely heavily on UHF stations as repeaters or as a local presence in large cities where VHF spectrum is largely already full. The handful of digital terrestrial television stations currently on-air in Canada as of 2008^[update] are also all UHF broadcasts.

Digital Audio Broadcasting, deployed on a very limited scale in Canada in 2005, uses UHF frequencies in the L band from 1452-1492 MHz. There are currently no VHF Band III digital radio stations in Canada as, unlike in much of Europe, these frequencies are among the most popular for use by television stations.¹

Ireland

In the Republic of Ireland, UHF was introduced in 1978 to augment the existing RTÉ One VHF 625-line transmissions and to provide extra frequencies for the new RTÉ Two channel. The first UHF transmitter site was Cairn Hill in Co. Longford, followed by Three Rock Mountain in South Co. Dublin. These sites were followed by Clermont Carn in Co. Louth and Holywell Hill in Co. Donegal in 1981. Elsewhere in Ireland, both the RTÉ channels are available on VHF. Since then RTÉ have migrated nearly all their low-power relay sites to UHF. TV3 and TG4 are transmitted entirely in UHF only. When Digital Terrestrial TV is introduced, it is intended to broadcast this on UHF only initially, although VHF allocations exist. VHF TV is likely to cease whenever the existing analogue broadcasts are switched off. The UHF band is also used in parts of Ireland for Television deflector systems bringing British television signals to towns and rural areas which cannot receive these signals directly

Japan

In Japan, an Independent UHF Station (ja:全国独立UHF放送協議会, Zenkoku Dokuritsu Yū-eichi-efu Hōsō Kyōgi-kai^?, literally National Independent UHF Broadcasting Forum) is one of a loosely-knit group of free commercial terrestrial television stations which is not a member of the major national networks keyed in Tokyo and Osaka.

Japan's original broadcasters were VHF. Although some experimental broadcasts were made as early as 1939, NHK (founded in 1926 as a radio network modelled on the BBC) began regular VHF television broadcasting in 1953. Its two terrestrial television services (NHK General TV and NHK Educational TV) appear on VHF 1 and 3 respectively in the Tokyo region. Privately-owned Japanese VHF TV stations were most often built by large national newspapers with Tokyo stations exerting a large degree of control over national programming.

The independent stations broadcast in analogue UHF, unlike major networks which were historically primarily broadcast in analogue VHF. The loose coalition of UHF independents is operated mostly by local governments or metropolitan newspapers with less outside control. Compared with major network stations, Japan's UHF independents have more restrictive programming acquisition budgets and lower average ratings; they are also more likely to broadcast single episode or short-series UHF anime (many of which serve to promote DVD's or other product tie-ins) and brokered programming such as religion and infomercials.

Japanese terrestrial television is in the process of switching entirely to digital UHF, with all analogue television (both VHF and UHF) planned to shut down in 2011.

Malaysia

UHF broadcasting was used outside Kuala Lumpur and the Klang Valley by private TV station TV3 in the late 80s, with the government stations only transmitting in VHF (Bands 1 and 3) and the 450 MHz range being occupied by the ATUR cellular phone service operated by Telekom Malaysia. The ATUR service ceased operation in the late 90s, freeing up the frequency for other uses. UHF was not commonly used in the Klang Valley until 1994 (despite TV3's signal also being available over UHF Channel 29, as TV3 transmitted over VHF Channel 12 in the Klang Valley). 1994 saw the introduction of the channel MetroVision (which ceased transmission in 1999, got bought over by TV3's parent company - System Televisyen Malaysia Berhad - and relaunched as 8TV in 2004). This was followed by Ntv7 in 1998 (also acquired by TV3's parent company in 2005) and recently Channel 9 (which started in 2003, ceased transmission in 2005, was also acquired by TV3's parent company shortly after, and came back as TV9 in early 2006). At current count, there are 4 distinct UHF signals receivable by an analog TV set in the Klang Valley: Channel 25 (8TV), Channel 29 (TV3 UHF transmission), Channel 37 (NTV7) and Channel 39 (TV9). Channel 35 is usually allocated for VCRs, decoder units (i.e. the ASTRO and MiTV set top boxes) and other devices that have an RF signal generator (i.e. game consoles).

United Kingdom

In the UK, UHF television began in 1964 following a plan by the GPO to allocate sets of frequencies for 625-lined television to regions across the country, so as to accommodate four national networks with regional variations (the VHF allocations allowed for only two such networks using 405 lines). The UK UHF channels would range from 21 to 68 (later extended to 69) and regional allocations were generally grouped close together to allow for the use of aerials designed to receive a specific sub-band with greater efficiency than wider-band aerials could. Aerial manufacturers would therefore divide the band into over-lapping groups; A (channels 21-34), B (39-53), C/D (48-68) and E (39-68). The first service to use UHF was BBC2 in 1964 followed by BBC1 and ITV (already broadcast on VHF) in 1969 and Channel 4/S4C in 1982. PAL colour was introduced on UHF only in 1967 (for BBC2) and 1969 (for BBC1 & ITV).

As a consequence of achieving maximum national coverage, signals from one region would typically over-lap with that of another, which was accommodated for by allocating a different set of channels in each adjacent area, often resulting in greater choice for viewers when a network in one region aired different programmes to the neighbouring region.

Initial uptake of UHF television was very slow: Differing propagation characteristics between VHF and UHF meant new additional transmitters needed to be built, often at different locations to the then-established VHF sites, and generally with a larger number of relay stations to fill the greater number of gaps in coverage that came with the new band. This led to poor picture quality in bad coverage areas, and many years before the service achieved full national coverage. In addition to this, the only exclusively UHF service, BBC2, would run for only a few hours a day and comprised of alternative programming for minority audiences in contrast to the more popularist schedules of BBC1 and ITV. However the 1970s saw a large increase in UHF TV viewing while VHF took a significant decline: The appeal of colour, which was never introduced to VHF (despite preliminary plans to do so in the late 1950s and early 1960s) and the fall in television prices saw most households use a UHF set by the end of that decade. With the second and last VHF television service having launched in 1955, VHF TV was finally decommissioned for good in 1985 with no plans for it to return to use.

The launch of Channel 5 in 1997 added a fifth national television network to UHF, requiring deviation from the original frequency allocation plan of the early 1960s and the allocation of UHF frequencies previously not used for television (such as UK Channels 35 and 37, previously reserved for RF modulators in devices such as domestic VCRs, requiring an expensive VCR re-tuning programme funded by the new network). A lack of capacity within the band to accommodate a fifth service with the complex over-lapping led to the fifth and final network having a significantly reduced national coverage compared to the other networks, with reduced picture quality in many areas and the use of wide-band aerials often required.

The launch of digital terrestrial television in 1998 saw the continued use of UHF for television, with six multiplexes allocated for the service, all within the UHF band. However analogue transmissions have been planned to cease completely by 2012 after which time it is uncertain as to whether the vacated capacity will be used for additional digital television services or put into alternative use, such as mobile telecommunications or internet services.

United States

Television

On December 29, 1949, KC2XAK of Bridgeport, Connecticut, became the first UHF television station to operate on a regular daily schedule. The first commercially licensed UHF television station on the air was KPTV/Channel 27 (now VHF Channel 12) in Portland, Oregon, on September 18, 1952. The station even used much of the equipment, including the transmitter, from KC2XAK, which was delivered by high-speed freight train.

Hopes that UHF would allow dozens of television stations in every media market were thwarted by poor image frequency rejection in superheterodyne tuners with 45.75 MHz intermediate frequency. Adjacent-channel rejection and selectivity were also abysmal in early tuner designs, to the point that local UHF TV stations were routinely being assigned a minimum of six channels apart. These shortcomings led to "UHF taboos," which limited each area to only modestly more UHF than VHF stations, despite the much larger number of channels.²

In the United States, UHF stations (broadcast channels above 13) originally gained a reputation for being locally owned, less polished and professional, not as popular, and having weaker signal propagation than their VHF counterparts (channels 2 through 13). Antenna manufacturers would rate their top-of-the-line deep-fringe models commonly as "100 miles VHF/60 miles UHF"; TV manufacturers would treat UHF tuners as optional-extra items until the All-Channel Receiver Act forced their inclusion as standard in 1964.

While UHF has been available to US television broadcasters since 1952, affiliates of the four major US television networks (NBC, CBS, ABC and DuMont) continued to transmit their programs primarily through VHF. A major city often could have three VHF allocations, although availability is limited by the entire VHF band only having twelve television channels and by restrictions intended to avoid assignment of adjacent channel stations in the same city. These initial VHF allocations were already all in use by the 1950s in most of the key markets, usually by the "big three" commercial networks, leaving few open VHF channels.

With the most powerful broadcasters all on VHF, most UHF stations that operated in major population centers of the USA were unable to obtain network affiliation and thus were independent stations.³ Others had to affiliate with weaker networks (such as fourth-ranked DuMont, which operated from 1946-1956). The movie UHF, starring "Weird Al" Yankovic and Michael Richards, parodied the phenomenon.

A notable exception existed in mid-sized television markets within the United States which were too close to the outer fringe of the broadcast range of large-city VHF stations to qualify for their own VHF broadcasts. No VHF channels were available in these areas, as any full-power VHF allocation would encounter problems of interference from overlapping broadcast ranges. The FCC therefore granted some mid-sized cities only UHF licenses (even for the big three networks), because of the vastly greater number of available channels (originally 70 total UHF channels vs. 12 total VHF). These communities, known as UHF islands, include cities like South Bend, Indiana, Elmira, New York, Scranton, Pennsylvania and Springfield, Massachusetts. Other small cities found that only one VHF channel was open and any additional programming would need to be provided either by UHF, by distant stations or by low power television.

ABC and the short-lived DuMont, being smaller and less prosperous networks, did have a number of UHF affiliates,⁴ National Educational Television and the later PBS had even more.

The original SIN, which was established in 1962 as the predecessor of the modern Univisión network, was built primarily by UHF broadcasters such as charter stations KWEX-TV 41 San Antonio and KMEX-TV 34 Los Angeles.

Ultimately, UHF was to become a means to obtain programming which was not being provided by the "big three" commercial networks; educational services like PBS, religious broadcasting and Spanish language or multilingual broadcasts all relied primarily on UHF to offer their unique programming alternatives. All New York-licensed educational stations, for instance, are on channel 16 or higher.

A large number of very small UHF TV transmitters continue to operate with no programming or commercial identity of their own, merely retransmitting signals of existing full-power stations to a smaller area poorly covered by the main VHF signal. Such transmitters are called "translators" rather than “stations”. The smallest, owned by local municipal-level groups or the originating TV stations, are numbered sequentially - W or K, followed by the channel number, followed by two sequentially-issued letters, yielding a "translator callsign" in a generic format which appears K14AA through W69ZZ. Translators and repeaters also exist on VHF channels, but infrequently and with stringently-limited power as the VHF spectrum is already crowded with full-power network stations in most regions.

The translator band, UHF TV channels 70-83, consisted mostly of these small repeaters; it was removed from television use in 1983. The 804-890MHz band segment is now primarily used by mobile telephones.

The number of major independent stations has declined as many have joined or formed new networks. The DuMont owned-and-operated station group Metromedia was acquired by News Corporation in 1986 and used as the foundation to relaunch a fourth commercial network which obtained affiliation with many former big-city independent stations as Fox TV.

While largely built from former independents and UHF stations in its early years, Fox had the large programming budgets that the original DuMont lacked. It ultimately was able in some markets to draw existing long-standing VHF affiliates away from established big-three networks, outbidding CBS for National Football Conference programming in 2004 and attracting many of that network's affiliates. Various smaller networks were created with the intent to follow in its footsteps, often assembling a fledgling network by affiliating with a disparate collection of formerly-independent UHF stations which otherwise would have no network programming.

Fox launched in 1986. UHF (film) parodied a fictional UHF 62 station in 1989. By 1994, New World Communications was moving its established stations from CBS to Fox affiliations in multiple markets, including WJBK-TV 2 Detroit. In many cases, this pushed CBS onto UHF; "U-62", the new home of CBS in Detroit, became CBS owned-and-operated station WWJ-TV in 1995.

The distinction between UHF and VHF characteristics has declined in importance with the emergence of additional broadcast television networks (Fox, The CW, MyNetworkTV, Univision, Telemundo and ION), and the decline of direct OTA reception. The concentration of media ownership, the proliferation of cable and satellite television and the digital television transition have contributed to the quality equalization of VHF and UHF broadcasts. While virtual channel numbering schemes routinely display channel numbers like "2.1" or "6.1" for individual North American terrestrial HDTV broadcasts, these are more often than not actually UHF signals.

UHF stations have also been increasing their effective radiated power, with some as high as five million watts analog or one megawatt digital, in order to better rival their more-established VHF counterparts. The higher maximum power levels for UHF stations (compared to those applied to digital stations in the already-crowded VHF bands) can make UHF well-adapted to digital broadcasting in many communities.

The majority of digital TV stations currently broadcast their over-the-air signals in the UHF band, either because VHF is already filled with analogue TV or because of severe issues with impulse noise on digital low-VHF channels. Many equipment vendors therefore use "HDTV antenna" or similar branding as all but synonymous to "UHF antenna". In some US markets, such as Syracuse, New York, there will be no stations returning to VHF after digital transition.

The one remaining limitation of UHF, that of a greatly-reduced ability for signals to travel great distances in the presence of obstacles due to terrain, can potentially be overcome by digital stations by the use of distributed transmission systems, in which multiple UHF transmitters can be combined and synchronised to produce a tailored coverage area pattern rivalling that of a single full-power VHF transmitter. While the US Federal Communications Commission authorisation to use DTS on anything more than an experimental basis came in November 2008, too late for sites to be acquired and transmitters built before the February 17, 2009 end of US digital transition, it is likely that more of these distributed UHF transmission systems will be constructed by broadcasters in the years to come in order to get digital and high-definition television out to a wider audience.

Radio, mobile and non-broadcast applications

The Family Radio Service and General Mobile Radio Service use the 462 and 467 MHz areas of the UHF spectrum. There is a considerable amount of lawful unlicensed activity (cordless phones, wireless networking) clustered around 900 MHz and 2.4 GHz. These ISM bands - open frequencies with a higher unlicensed power permitted for use originally by Industrial, Scientific, Medical apparatus - are now becoming some of the most crowded in the spectrum because they are open to everyone.

The 2.45GHz frequency, readily absorbed by water, is the standard for use by microwave ovens.

The spectrum from 806 MHz to 890 MHz (UHF channels 70-83) was taken away from TV broadcast services in 1983, primarily for analogue mobile telephony. In February 2009, as part of the transition from analog to digital over-the-air broadcast of television, the spectrum from 698 MHz to 806 MHz (UHF channels 52-69) will also no longer be used for TV broadcasting. Channel 55, for instance, was sold to Qualcomm for their MediaFLO service, which is resold under various mobile telephone network brands. Some US broadcasters have been offered incentives to vacate this channel early, permitting its immediate mobile use.

The FCC's scheduled auction for this newly-available spectrum was completed in March 2008. ⁵

Frequency allocation

Australia

• UHF Citizens Band: 476.425–477.400 MHz

Canada

• 470-804 MHz: Terrestrial television (with select channels in the 700MHz band left vacant)
• 1452-1492 MHz: Digital Audio Broadcasting (L band)⁶
• Many other frequency assignments for Canada and Mexico are similar to their US counterparts

United Kingdom

• 380–395 MHz: Terrestrial Trunked Radio (TETRA) service for emergency use
• 430–440 MHz: Amateur radio (ham - 70 cm band)
• 606–614 MHz: Protected for radio-astronomy
• 470–862 MHz: TV channels 21–69 (channel 36 used for radar, channel 38 used for radio astronomy, channel 69 used for licenced and licence exempt wireless microphones, channels 31-40 and 63-68 to be released and may be made available for other uses by Ofcom. Public consultation due December 2006)
• 1240–1316 MHz: Amateur radio (ham - 23 cm band)
• 1880–1900 MHz: DECT Cordless telephone
• 2310–2450 MHz: Amateur radio (ham - 13 cm band)

United States

A brief summary of some UHF frequency use:

• 300–420 MHz: Government use, including meteorology and federal two-way use
• 420–450 MHz: Government radiolocation and amateur radio (ham - 70 cm band)
• 450–470 MHz: UHF business band, General Mobile Radio Service, and Family Radio Service 2-way "walkie-talkies", public safety
• 470–512 MHz: TV channels 14–20
• 512–698 MHz: TV channels 21–51 (channel 34 used sometimes for radar, channel 37 used for radio astronomy)
• 698–806 MHz: TV channels 52–69 (was auctioned in March 2008; bidders will get full use once conversion to digital TV has been accomplished which is scheduled for February 17, 2009)
• 806–824 MHz: Pagers (formerly TV channels 70–72)
• 824–849 MHz: AMPS A & B franchises, terminal (mobile phone) (formerly TV channels 73–77)
• 849–869 MHz: Public safety 2-way (fire, police, ambulance — formerly TV channels 77–80)
• 869–894 MHz: AMPS A & B franchises, base station (formerly TV channels 80–83) (one translator is still in use on channel 83)
• 902–928 MHz: ISM band: cordless phones and stereo, radio frequency identification, datalinks, amateur radio (33 cm band)
• 928–960 MHz: Mixed studio-transmitter links, mobile 2-way, paging, other.
• 1240–1300 MHz: Amateur radio (ham - 23 cm band)
• 1452–1492 MHz: Military use (therefore not available for Digital Audio Broadcasting, unlike Canada/Europe)
• 1850–1910 MHz: PCS mobile phone—order is A, D, B, E, F, C blocks. A, B, C = 15 MHz; D, E, F = 5 MHz
• 1920–1930 MHz: DECT Cordless telephone
• 1930–1990 MHz: PCS base stations—order is A, D, B, E, F, C blocks. A, B, C = 15 MHz; D, E, F = 5 MHz
• 2300–2310 MHz: Amateur radio (ham - 13 cm band, lower segment)
• 2310–2360 MHz: Satellite radio (Sirius and XM)
• 2390–2450 MHz: Amateur radio (ham - 13 cm band, upper segment)
• 2400–2483.5 MHz: ISM, IEEE 802.11, 802.11b, 802.11g Wireless LAN, IEEE 802.15.4, Bluetooth
• 2450 MHz: Microwave oven

References

See also

• Australasian TV frequencies
• Bluetooth
• Broadcast television systems
• Channel 37
• Digital Audio Broadcasting and its regional implementations
• Digital terrestrial television
• Knife-edge effect
• L-band
• North American broadcast and cable television frequencies
• Television channel frequencies
• Terrestrial television
• Thing (listening device)
• UHF CB
• Very High Frequency
• Wi-fi

External links

• U.S. cable television channel frequencies
• TVTower.com - Commercial Television Frequencies

• Tomislav Stimac, "Definition of frequency bands (VLF, ELF... etc.)". IK1QFK Home Page (vlf.it).